Lacey V. Murrow Memorial Bridge

Vorlage:Infobox Bridge The Lacey V. Murrow Memorial Bridge is a floating bridge that carries the eastbound lanes of Interstate 90 across Lake Washington from Seattle to Mercer Island, Washington. It is the third longest floating bridge in the world at Vorlage:Convert, whereas the second longest is the Evergreen Point Floating Bridge just a few miles to the north on the same lake, built 23 years later. The longest is the Hood Canal Bridge, also in Washington State, about 30 miles to the Northwest of the Evergreen Point Floating Bridge.

Along with the east portals of the Mount Baker Ridge Tunnel, the bridge is an official City of Seattle landmark. An opening span is located at the center of the bridge to allow a horizontal opening of 202 feet for major waterborne traffic. It also has elevated fixed spans at the termini which can accommodate free passage of boats with 29 feet of vertical clearance.

History

The bridge was the brainchild of George Lightfoot, who came to be called the "father of the bridge". Lightfoot began campaigning for the bridge in 1930, enlisting the support of Miller Freeman. The original two-way, four-lane toll bridge was designed by the engineer Homer Hadley (1885-1967) and constructed of reinforced concrete in 1940. The construction cost for the project was in the order of $9,000,000 including approaches. It was partically financed by a bond issue of $4,184,000. Tolls were removed in 1946. It sank in a storm on November 25, 1990, while it was undergoing refurbishing & repair. The current bridge was built in 1993. The eponymous Lacey V. Murrow was the second Director of the Washington State Highway Department and a highly decorated US Air Force officer who served in World War II. He was the oldest brother of CBS commentator Edward R. Murrow.

Formerly known as the "Lake Washington Floating Bridge", the original bridge was built under a 1-1/2 year contract awarded to the Puget Sound Bridge and Dredging Company (the project was led by engineer Peter John Jensen) in the amount of $3,254,000. It included a movable span that could be retracted into a pocket in the center of the fixed span to permit large boats to pass. This design resulted in a roadway "bulge" that required vehicles to swerve twice across polished steel joints as they passed the bulge. A "reversible lane" system, indicated by lighted overhead lane control signals with arrow and 'X' signs, compounded the hazard by putting one lane of traffic on the "wrong" side of the bulge at different times of day in an effort to alleviate rush-hour traffic into or out of Seattle. There were many serious collisions on the bridge. The problems grew worse as the traffic load increased over the years and far outstripped the designed capacity. Renovation or replacement were essential and a parallel bridge, the Homer M. Hadley Memorial Bridge, was completed in 1989.

1990 disaster

View northeast of bridge, west approach and Mount Baker Tunnel

In 1990, while under construction, the original bridge sank due to a combination of human errors and decisions. The process started because the bridge needed resurfacing and was to be widened by means of cantilevered additions in order to meet the necessary lane-width specifications of the Interstate Highway System. The Washington State Department of Transportation (WSDOT) decided to use hydrodemolition (high-pressure water) to remove unwanted material (the sidewalks on the bridge deck). Water from this hydrodemolition was considered contaminated under environmental law and could not be allowed to flow into Lake Washington. Engineers then analyzed the pontoons of the bridge, and realized that they were over-engineered and the water could be stored temporarily in the pontoons. The watertight doors for the pontoons were therefore removed.

A large storm on November 22, 23, and 24, 1990 (the Thanksgiving holiday weekend) filled some of the pontoons with rain and lake water. On November 24, workers noticed that the bridge was about to sink, and started pumping out some of the pontoons. However, on November 25, Vorlage:Convert of the bridge sank, dumping the contaminated water into the lake along with tons of bridge material. The bridge sank when one pontoon filled and dragged the rest down because they were cabled together and there was no way to separate the sections under load. Fortunately, no one was hurt or killed, since the bridge was closed for renovation and the sinking took some time. All of the sinking was captured on film and shown on live TV.

Precedents and lessons for the future

WSDOT lost another floating bridge, the Hood Canal Bridge, about a decade earlier under similar circumstances, and it is now known that another major floating bridge in Washington, the Evergreen Point Floating Bridge, is under-engineered for local environmental conditions. due to a combination of human errors and decisions.

See also

• Homer M. Hadley Memorial Bridge

External links

• Bridge Camera, includes some weather information
• Report from engineering firm analyzing the sinking of the bridge
• HAER Survey number HAER WA-2 - Lacey V. Murrow Memorial Floating Bridge, Spanning Lake Washington at I-90, Seattle, King County, WA
• History Link on the bridge
• Department of Transportation photos of sinking
• King-5 television video of the sinking